Cathode structure for magnetrons



March 1, 1949. I I c 2,463,398

CATHODE STRUCTURE FOR MAGNETRONS Filed July 9, 1945 IN V EN TOR.

POLYKARP KUSCH ATTORNEY Patented Mar. 1, 1949 CATHODE STRUCTURE FOR MAGNETRONS Polykarp Kusch, New York, N. Y., assignor to the United States of America as represented by the Secretary of War Application July 9, 1945, Serial No. 604,071

6 Claims. 1

This invention relates in general to electrical apparatus and more particularly to magnetron oscillators.

The common type of magnetron oscillating tube employs an indirectly heated cathode which is conventionally supported by lead-in wires. These lead-in wires carry the currents used to heat the cathode structure and consequently a magnetic field is set up about each wire. When alternating current is used as a source of heat energy, the alternating magnetic field thus set up may cause mechanical vibration in the cathode or supporting structure. If such vibration occurs over a prolonged period of time, the cathode structure may suffer damage from mechanical failure of the component parts resulting in shortened tube life and the necessity for frequent replacement.

Accordingly, it is an object of the present invention to provide a cathode lead-in structure about which no magnetic field is set up.

Another object is to increase tube life by obviating mechanical failure due to cathode vibration as described hereinabove.

Still another object is to provide a cathode supporting structure which is mechanically strong.

The invention will best be understood with reference to the following specification, claims, and drawings, in which the only figure illustrates a cross-sectional view of one embodiment of the invention, the cross section being taken along the axes of a magnetron and of the cathode lead structure.

Briefly, the invention lies in the use of a coaxial cathode support and lead-in structure wherein the heater currents flow in one direction on the central conductor of a coaxial line and in the opposite direction on. the outer conductor. In this fashion, the resulting magnetic fields are confined within the coaxial line itself and no field exists about the cathode support to cause vibrational forces.

Referring now to the drawing, it discloses a sectional View of the magnetron including only a portion of a wave guide output circuit 20 and a portion of the permanent magnets 22 and 24, these elements not being fully illustrated because the invention resides in the cathode structure, the latter being fully illustrated in the sectional view. The magnetron is mounted between permanent magnets 22. and 24, the faces of the magnets engaging soft iron pole-pieces 26 and 28, which are silver-soldered at 29 and 30 to a copper shell 3|, thus completing the gas-tight connection between. the shell and the pole-pieces. While the wave guide 20 is only partially illustrated in the figure, it is provided, in the portion which is not illustrated in the drawing, with a gas-tight electrical window which seals-off the inner chamber of the magnetron from atmospheric pressure. The anode-cathode structure of the magnetron is mounted between the pole-pieces in spaced relationship with respect to the pole-pieces. An anode 32 is held fixedly by shell 3|, the shell being sufficiently high to provide two end spaces above and below the cathode-anode assembly. The cathode structure illustrated in the figure is of the radial type, a tungsten rod 5 being used for supporting the cathode cylinder 33 in central position with respect to the anode. The cathode is of usual indirect heater type, a coil 34 being inserted in the hollow portion of the cathode cylinder 33. A concentric line is used for connecting the heater to a source of heater potential 35. This line consists of the previously mentioned central tungsten rod 5, a glass insulating sleeve 1, and a copper sleeve 8, the tungsten rod being connected to the cathode by means of a molybdenum or copper jumper 35 while the outer conductor of the concentric line is connected to the heater coil by means of a similar jumper 38. The opposite end of the heater coil is connected to the cathode cylinder 33, which completes the circuit of the heater coil. A tungsten rod 5 has glass beads 6 and 1 formed around it. Over bead l is placed a copper sleeve 8, an extension 9 of which is employed to make electrical connection with the cathode heater element 34. A metal ferrule I0 is placed over sleeve 8, its inner diameter being sufficiently greater than the outer diameter of sleeve 8 to maintain adequate voltage clearance for the voltage existing between. sleeve 8 and ferrule l0. Ferrule I0 is so shaped as to fit snugly into a similarly shaped opening in the magnetron shell 3!. A wire I3 is wound around sleeve 8 making electrical connection therewith and is brought out through a supporting glass bead H to a point where heater voltage 35 may be readily applied between wire [3 and rod 5. A glass shell l5, sealed at one end to the beads 6 and I4 and at the other end to a metallic sleeve 16 having a coefficient of expansion equal to the same coefficient of glass. Sleeve It in turn is seated inferrule 10. allows evacuation of the magnetron and the volume immediately surrounding the cathode supporting structure.

It can be seen that rod 5 and sleeve 8 form a coaxial line whose dielectric is the glass layer 1. Rod 5 and wire I3 provide all necessary connections for the cathode, the former affording the connection for the cathode and one terminal Hence I claim all such modifications and adapta:

tions as may fall fairly within the spirit and scope of the hereinafter appended claims.

What I- claim. is:

1. Apparatus for supporting the cathode of an electron tube and for conducting an alternating current energy to the heater element of said cathode through a magnetic fieldwithout producing vibratory interaction between said apparatus and said magnetic field comprising a first conductor, first and second glass beads formed in tandem around said first conductor, a second conductor tubular in shape and fitting closely over said first glass bead and concentric to said firstconductor, said first and second conductors together with said first glass bead forming a coaxial line, a source of magnetic field, said field surrounding said coaxial conductor means attaching the cathode to said first conductor, means attaching said heater element to said first and second conductors, a ferrule of conducting material positioned concentric to said first conductor attaching the apparatus to an electron tube with which it is to be used, and a third conductor connected to said second conductor for application of said alternating current energy to said concentric line and to said heater eiement without subjecting said cathode to said vibratory interaction.

2. Apparatus for supporting an indirectly heated cathode and for energizing a heater element of said cathode comprising an external source of alternating current, a first conductor connected to said cathode, a second tubular conductor placed concentrically with respect to said first conductor, two jumpers connecting said heater element to said first and second conductors and mechanically supporting iSEtld cathode, a source of magnetic field producing a magnetic field surrounding said first and second conductors, and terminals for connecting said source to said first and second conductors, for said energizing of said heater element without producing mechanical oscillation of said apparatus through otherwise possible interaction between said field and the current flowing through said conductors, said interaction being prevented because of the concentric-mounting of said first and second conductors.

3. A thermionic tube including a degassed vessel, an indirectly heated cathode within said vessel, a heater for said cathode, a source of magnetic field producing a magnetic field surrounding said cathode and said heater, a concentric line having inner and outer conductors insulated from each other and protruding into said vessel through said field, a first connection between said inner conductors and said cathode, said connection rigidly supporting said cathode, a second connection between the outer conductor and the other end of said heater, said first and second connectionscompleting the electrical circuit of said cathode and of said heater, a ferrule forming ages-tight joint with said vessel, a ring forming a gas-tight joint with said, fea-ule, and a glass seal connected to said ring, the outer end of said concentric line protruding through said glass seal and forming a gas-tight joint with said glass seal, said vessel supporting said concentric line and said cathode through said ferrule, ring and said glass seal, the concentric nature of said line permitting alternating current energization of said cathode without subjecting said cathode to mechanical oscillations because'of otherwise possibleinteraction between said'field and said alternating-current; i 4

4. A cathode structure for a thermionic tube comprising a cathode and a cathode heater placed in a magnetic field, a concentric line having inner and outer conductors, insulated from each other and passing through said field, and mechanically rigid jumpers between said cathode heater, and said conductors completing the electrical circuit of said cathode, and said heater said jumpers supporting and rigidly holding said cathode, said concentric line extending substantially up to said cathode for nullifying the interaction between said magnetic field and the alternating fields due to the alternating cathode heating current flowing through said line.

5. A magnetron comprising an anode, end spaces above and below said anode, a cathode symmetrically disposed with respect to said anode defining the interaction space between said cathode and said anode, said anode and said cathode being exposed to a magnetic field substantially parallel to the axis of said cathode, a

radially disposed concentric line whose axis is' substantially perpendicular to said magnetic field, said line terminating in one of said end spaces, and having inner and outer conductors insulated from each other, and mechanically rigid connections between said cathode and said conductors completing the electrical circuit of said cathode and mechanically supporting said cathode, said concentric line nullifying the interaction between said magnetic field and the alternating field due to the alternating cathode heating current flowing through said conductors and said connections.

6. A magnetron including a magnetic field, an anode, end spaces above and below said anode, an indirectly heated cathode centrally mounted with respect to said anode, a concentric line having inner and outer conductors protruding into one of the end spaces of said magnetron, said line being radially mounted with respect to said anode and said cathode, mechanically rigid connections between said cathode and the inner end of the concentric line protruding into one of the end spaces of said magnetron, said connections completing the cathode and the heater connections of said cathode and mechanically supporting said cathode, an outer shell supporting said anode, a ferrule forming a gas-tight joint with said shell, and a glass seal connected to said ferrule and forming a gas-tight joint with said fer- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENIS Number Name Date 1,995,478 Lauritsen Mar. 26, 1935 2,157,952 Dallenbach May 9, 1939 2,167,201 Dallenbach July 25, 1939 2,309,966 Litton Feb. 2, 1943 2,345,642 Varian et al Apr. 4, 1944 2,353,743 McArthur July 18, 194'; 2,406,277 Bondley Aug. 20, 1946 

